Intracellular Ca2+ plays a pivotal role in various cell functions, ranging from exocytosis and contraction to gene expression and cell differentiation, proliferation and apoptosis. Ca2+ entry into cells, particularly in non-excitable cells, can be mediated via store-operated Ca2+ channel (s) (SOC). Following Ca2+ release from the intracellular stores, SOC mediate Ca2+ influx from the extracellular space to generate sustained increases in intracellular Ca2+ concentration and replenish the internal Ca2+ stores. The molecular mechanism of SOC activation and the molecular identity of SOC remains elusive. Members of TRP (Transient Receptor Potential) channels, an emerging class of Ca2+-permeable cation channel superfamily, are likely candidates for SOC (reviewed in Trends Neurosci, 23, 159-166, (2000)).
Human mutations in the genes involved in intracellular Ca2+ handling result in visual defects, diabetes mellitus, disorders in the skin, skeletal-muscle, nervous, cardiac and vascular systems (reviewed by Missiaen et al., 2000). In addition to the well characterized voltage-dependent Ca2+ channels, Ca2+ pumps and Ca2+-permeable ligand-gated channels, TRPC (Transient Receptor Potential Channels) is an emerging class of Ca2+-permeable cation channel superfamily. All of the channels in this family contain a six-trans-membrane domain although various cellular mechanisms have been implicated in their functions.
Following the identification of the founding member of this family, dTRP, from the Drosophila mutants trp whose photoreceptors failed to generate a sustained receptor potential in response to intense sustained light (Neuron 8, 643-651, (1992)), mammalian homologues have been cloned and all of them contain a six-trans-membrane domain followed by a TRP motif (XWKFXR, SEQ ID NO:), the diagnosed feature of the TRP family of proteins. The mutant fly showed a reduced Ca2+ selectivity of the light response and the channel activity of DTRP depended on PLC activation was also demonstrated.
Based on their homology, they are divided into three subfamilies: short (s), osm (o) and long (l). New nomenclature for each subfamily has recently been proposed and is as follows: TRPC (canonical), TRPV (vanilloid), and TRPM (melastatin) (Mol. Cell. 9, 229-231, (2002)). The sTRPC subfamily includes TRP1-7. Although the specific physiological function of each isoform remains to be assigned, it is generally believed that they may be involved in Ca2+ entry after activation of receptors coupling to PLC. The TRP2 is specifically expressed in vomeronasal organ and involved in pheromone sensory signaling (Liman, et al., 1999). TRP1 and TRP6 are functioned in vascular smooth muscle cells and may play a role in controlling smooth muscle tone, arteriosclerosis and neointimal hypoerplasia (Inoue et al., 2001; Xu & Beech, 2001). It has been shown that TRP4−/− mice lack an endothelial store-operated Ca2+ current, which leads to reduced agonist-dependent vasorelaxation (Freichel et al., 2001).
The first member of oTRPC Subfamily is OSM-9 cloned from C. elegans. It is involved in responses to odorants, high osmotic strength, and mechanical stimulation. Recently, several mammalian homologues including vanilloid receptor (VR1) and vanilloid receptor-like receptor (VRL-1), which may have functions in pain and heat perception (Caterina, 1999; Caterina et al., 2000). VR1 has also been shown to be the receptor of anandamide and mediating its vasodilation effect (Zygmunt et al., 1999). OTRPC4 is an osmotically activated channel and a candidate osmoreceptor, may be involved in regulation of cellular volume (Strotmann et al., 2000). CaT1 & ECaC1 may be the calcium-release-activated calcium channel and involved in Ca2+ reabsorption in intestine and kidney (Peng, et al, 1999; Yu et al., 2001).
The function of the lTRPC is less clear. The cloned mammalian lTRPC includes melastatin1/MLSN1/LTRPC1, MTR1/LTRPC5, TRPC7/LTRPC2 and TRP-P8. It is known that melastatin 1 is down regulated in metastatic melanomas (Duncan et al., 1998) and MTR1 is associated with Beckwith-Wiedemann syndrome and a predisposition to neoplasias (Prawitt et al., 2000). TRPC7 is mapped to the chromosome region linked to bipolar affective disorder, nonsyndromic hereditary deafness, Knobloch syndrome and holosencephaly (Nagamine et al., 1998). TRP-P8 is a prostate-specific gene and up-regulated in prostate cancer and other malignancies (Tsavaler et al., 2001). A recently cloned TRP-PLIK/hSOC-2/hCRAC-1 exhibits a very interesting feature in that it is a bi-functional protein with kinase and ion channel activities (Runnels et al., 2001). Additionally, a very long TRPC homologue NOMPC was found in Drosophila and C. elegans. NOMPC was identified as a mechanosensitive channel that can detect sound, pressure or movement changes (Walker et al., 2000).
Members of the TRPM subfamily are characteristic of their unusually long cytoplasmic tails at both ends of the channel domain and some of the family members contain an enzyme domain at the C-terminal region. Despite their similarities of structure, TRPMs have been implicated in a variety of biological functions. TRPM1 is found to be down-regulated in metastatic melanomas (Cancer Res. 58, 1515-1520, (1998)). TRPM2 is a Ca2+-permeable channel that contains an ADP-ribose pyrophosphatase domain and can be activated by ADP-ribose, NAD (Nature 411, 595-599, (2001); and Science 293, 1327-1330, (2001)) and changes in redox status (Mol. Cell. 9, 163-173, (2002)). TRPM2 is mapped to the chromosome region linked to bipolar affective disorder, nonsyndromic hereditary deafness, Knobloch syndrome and holosencephaly (Genomics 54, 124-131, (1998)). Two splice variants of TRPM4 have been described. TRPM4a is predominantly a Ca2+ permeable channel (Proc. Natl. Acad. Sci. U.S.A. 98, 10692-10697, (2001); whereas TRPM4b conducts monovalent cations upon activation by changes in intracellular Ca2+ (Cell 109, 397-401, (2002)). TRPM5 is associated with Beckwith-Wiedemann syndrome and a predisposition to neoplasias (Mol. Genet. 9, 203-216, (2001)). TRPM7, another bi-functional protein, has kinase activity in additional to its ion channel activity. TRPM7 is regulated by Mg2+-ATP and/or PIP2, and required for cell viability (Science 291, 1043-1047, (2001); Nature 411, 690-695, (2001); and Nat. Cell Biol. 4, 329-36, (2002)). TRPM8 is up-regulated in prostate cancer and other malignancies (Cancer Res. 61, 3760-3769, (2001)). Recently, it has also been shown to be a receptor that senses cold stimuli (Nature 416, 52-58, (2002); and Cell 108, 705-715, (2002)).
Characterization of the LTRPC3 polypeptide of the present invention led to the determination that it is involved in the modulation of the FEN1 DNA base-excision repair/proliferation modulating protein, either directly or indirectly.
In mammalian cells, single-base lesions, such as uracil and abasic sites, appear to be repaired by at least two base excision repair (BER) subpathways: “single-nucleotide BER” requiring DNA synthesis of just one nucleotide and “long patch BER” requiring multi-nucleotide DNA synthesis. In single-nucleotide BER, DNA polymerase beta (beta-pol) accounts for both gap filling DNA synthesis and removal of the 5′-deoxyribose phosphate (dRP) of the abasic site, whereas the involvement of various DNA polymerases in long patch BER is less well understood.
Flap endonuclease 1 (Fen1) is a structure-specific metallonuclease that plays an essential function in DNA replication and DNA repair (Tom, S., Henricksen, L, A., Bambara, R, A, J. Biol, Chem., 275(14):10498-505, (2000)). It interacts like many other proteins involved in DNA metabolic events with proliferating cell nuclear antigen (PCNA), and its enzymatic activity is stimulated by PCNA in vitro by as much as 5 to 50 fold (Stucki, M., Jonsson, Z, O., Hubscher, U, J. Biol, Chem., 276(11):7843-9, (2001)). Recently, immunodepletion experiments in human lymphoid cell extracts have shown long-patch BER to be dependent upon FEN1 (Prasad, R., Dia, G, L., Bohr, V, A., Wilson, S, H, J. Biol, Chem., 275(6):4460-6, (2000)). In addition, FEN1 has also been shown to cooperate with beta-pol in long patch BER excision and is involved in determining the predominant excision product seen in cell extracts. The substrate for FEN1 is a flap formed by natural 5′-end displacement of the short intermediates of lagging strand replication. FEN1 binds to the 5′-end of the flap, tracks to the point of annealing at the base of the flap, and then cleaves the substrate (Tom, S., Henricksen, L, A., Bambara, R, A, J. Biol, Chem., 275(14):10498-505, (2000)).
The FEN1 is also referred to as Rad27. FEN1 plays a critical role in base-excision repair as evidenced by Saccharomyces cerevisiae FEN1 null mutants displaying an enhancement in recombination that increases as sequence length decreases (Negritto, M, C., Qiu, J., Ratay, D, O., Shen, B., Bailis, A, M, Mol, Cell, Biol., 21(7):2349-58, (2001)). The latter suggests that Rad27 preferentially restricts recombination between short sequences. Since wild-type alleles of both RAD27 and its human homologue FEN1 complement the elevated short-sequence recombination (SSR) phenotype of a rad27-null mutant, this function may be conserved from yeast to humans. Furthermore, mutant Rad27 and FEN-1 enzymes with partial flap endonuclease activity but without nick-specific exonuclease activity were shown to partially complement the SSR phenotype of the rad27-null mutant suggesting that the endonuclease activity of Rad27 (FEN-1) plays a role in limiting recombination between short sequences in eukaryotic cells. In addition, preliminary data from yeast suggests the FEN-1 deficiencies may result in genomic instability (Ma, X., Jin, Q., Forsti, A., Hemminki, K., Ku, R, Int, J. Cancer., 88(6):938-42, (2000)). More recently, FEN 1 null mutants results in the expansion of repetitive sequences (Henricksen, L, A., Tom, S., Liu, Y., Bambara, R, A, J. Biol, Chem., 275(22):16420-7, (2000)).
Aside from the role of FEN1 in base-excision repair, FEN1 has also been shown to play a significant role in modulating signal transduction in proliferating cells. This role is intricately associated with the role of FEN1 in DNA replication. Of particular significance is the observation that FEN1 is a nuclear antigen, that it is expressed by cycling cells, and that it co-localizes with PCNA and polymerase alpha during S phase. Fen1 expression is topologically regulated in vivo and is associated with proliferative populations (Warbrick, E., Coates, P, J., Hall, P, A, J. Pathol., 186(3):319-24, (1998)). Antibodies have been described by Warbrick et al. that specifically bind FEN1, the assays of which are hereby incorporated herein by reference.
In addition, experiments in S. cerevisiae using the novel immunosuppressant agent SR 31747 have shown that SR 31747 arrests cell proliferation by directly targeting sterol isomerase and that FEN 1 is required to mediate the proliferation arrest induced by ergosterol depletion (Silve, S., Leplatois, P., Josse, A., Dupuy, P, H., Lanau, C., Kaghad, M., Dhers, C., Picard, C., Rahier, A., Taton, M., Le, Fur, G., Caput, D., Ferrara, P., Loison, G, Mol, Cell, Biol., 16(6):2719-27, (1996)).
Using the above examples, it is clear the availability of a novel cloned transient receptor potential channel family provides an opportunity for adjunct or replacement therapy, and are useful for the identification of transient receptor potential channel agonists, or stimulators (which might stimulate and/or bias transient receptor potential channel function), as well as, in the identification of transient receptor potential channel inhibitors. All of which might be therapeutically useful under different circumstances.
The present invention also relates to recombinant vectors, which include the isolated nucleic acid molecules of the present invention, and to host cells containing the recombinant vectors, as well as to methods of making such vectors and host cells, in addition to their use in the production of LTRPC3, LTRPC3b, LTRPC3c, and LTRPC3e polypeptides using recombinant techniques. Synthetic methods for producing the polypeptides and polynucleotides of the present invention are provided. Also provided are diagnostic methods for detecting diseases, disorders, and/or conditions related to the LTRPC3, LTRPC3b, LTRPC3c, and LTRPC3e polypeptides and polynucleotides, and therapeutic methods for treating such diseases, disorders, and/or conditions. The invention further relates to screening methods for identifying binding partners of the polypeptides.